Fetal monitors of various types are widely used in the obstetrics field. Most of the devices provide to the clinician an indication of fetal heart rate (HR) as one item of data used by the clinician to evaluate overall fetal well-being. Other more sophisticated devices perform frequency analysis on heart rate time data to produce indications of heart rate variability (HRV), another very important item of data used to monitor fetal condition.
Typically, these frequency analysis devices collect fetal heart rate time data over relatively long periods of time. At the end of each period, a linear time-frequency representation, such as a short-term Fourier transform or a fast Fourier transform, is computed on the time data to obtain a frequency distribution for the data. In one such prior system, each time data window is 30-60 seconds in duration.
A significant drawback to these devices is that, because of the long time data window duration, or, equivalently, the low time resolution of the device, short term or transient variations in heart rate and/or heart rate variability cannot be detected. These transient changes can be indicators of significant fetal characteristics such as fetal breathing and should be considered in evaluating overall fetal well-being. Because these prior systems have long time windows, transient changes are not detected, and, therefore the often critically important fetal characteristics associated with the transient changes are not taken into consideration in the overall fetal evaluation.